Knife sharpener



FIG. 1 is a perspective view of a knife sharpener showing our new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a right end elevational view thereof;

FIG. 5 is a left end elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken lines in FIGS. 3 and 7 illustrate portions of the design that form no part of the claim. 

CLAIM The ornamental design for a knife sharpener, as shown and described. 